The present invention relates to live roller conveyors used to transport articles along a predetermined path and, more particularly, to zero pressure accumulation conveyors and brake assemblies therefor.
Live roller conveyors and, even more particularly, accumulation conveyors are well known in the art. Such accumulation conveyors have, in the past, employed various mechanisms for controlling the rotation of the conveyor rollers to allow them to be selectively rotated or stopped to accommodate accumulation of the articles being conveyed by the conveyors. The rollers are rotated to convey the articles to a collection or accumulation location and, once one or more of the articles have reached that location, the rollers are stopped to provide for accumulation.
One such mechanism is shown in U.S. Pat. No. 3,650,375 (Fleischauer et al). That patent discloses live rollers, each of which is driven by a resilient O-belt looped about a pulley beneath the rollers. The pulley is movable axially along a driven shaft. When articles are being conveyed by the rollers, the pulley axially slides along the driven shaft to assume a position in which it is frictionally engaged with the driven shaft to cause the pulley to rotate with the drive shaft and, thereby, drive the rollers by way of the O-belt. Once an article is accumulated at a desired location on the conveyor, movement of the article is prevented either by engagement of the article with a conveyor discharge gate or by contact of the article with a preceding article. When this latter condition occurs, the rollers beneath the article which has now stopped experience a frictional counter force on their cylindrical surfaces due to the weight of the overlying article which causes the axially movable pulleys to move axially along the driven shaft to such point that their frictional engagement with the driven shaft is no loner sufficient to allow the pulleys to rotate with the driven shaft, thereby causing the pulleys to slip relative to the driven shaft and to cease to impart driving force to the live rollers through the O-belts.
The aforementioned construction is perfectly acceptable in most uses. However, it relies to a principal extent upon some measure of restraining contact of the articles, either with a conveyor discharge gate or between the articles themselves. Such contact is of some concern, however, where the articles are extremely delicate, for example, electronic equipment in which extremely delicate handling of the articles is necessary to avoid damage. For such delicate equipment, it is desirable to eliminate all contact of the articles with a gate or with other articles to eliminate any possibility of impact or jarring of the equipment. In addition, such mechanisms rely upon frequent or continuous slippage of various elements of the drive system relative to other elements when the articles have reached their accumulation location. Such slippage may result in early wear and the need for early replacement of the elements.
Various mechanisms have been employed in the past for positively controlling the rotation of the driven shaft, either in combination with such slidable pulleys or otherwise, in an attempt to overcome at least some of the aforementioned disadvantages. One such mechanism employing a clutch assembly is shown in U.S. Pat. No. 3,840,110 (Molt et al). In that patent, several relatively complex clutching mechanisms are disclosed which operate to couple the driven shaft and its pulleys with a drive shaft to drive the driven shaft, its pulleys, O-belts and conveyor rollers when it is desired to move an article along the conveyor, but to positively uncouple the driven shaft in response to the actuation of suitable triggering mechanisms which sense the arrival of an article at a desired accumulation location. Although such clutching mechanisms minimize contact between the articles being conveyed and reduce frictional heat buildup and wear of the drive elements, such mechanisms are relatively complex with the attendant need to stock a large number of repair parts, and the increased difficulty of assembly and maintenance which always accompanies mechanisms of relatively complex construction.
Brake assemblies have also been employed in the past in conjunction with such conveyor drive and driven shafts. One such brake assembly is shown, for example, in U.S. Pat. No. 3,696,912 (Fleischauer et al). In that patent a brake assembly is disclosed which is mechanically actuated by a suitable trigger element which senses the presence of the article at its desired accumulation location. The trigger is mechanically coupled by a cable or chain which is connected to the brake assembly to cause the brake to engage a key on the driven shaft to lock the driven shaft against rotation. Although this mechanical key brake construction is, likewise, acceptable in a wide range of uses, it has the disadvantage of the need for relatively frequent maintenance and adjustment and some jarring of the elements and of the articles results from the positive key locking action.
The zero pressure accumulation conveyor and brake assembly of the present invention overcome the several aforementioned disadvantages of the prior constructions. A zero pressure accumulation conveyor and brake assembly constructed in accordance with the principles of the present invention minimize frictional heat and wear between the elements which slip relative to each other, thus resulting in a decrease in the need for maintenance and repair. In a zero pressure accumulation conveyor and brake assembly incorporating the principles of the present invention, positive and rapid braking action is imparted to the drive element of the conveyor to achieve rapid deceleration of the articles without damage to the articles, even though sufficient slip between the drive elements is retained with its attendant advantages. A zero pressure accumulation conveyor and brake assembly constructed in accordance with the principles of the present invention is safe, quiet and simple in construction, thereby substantially reducing the need for maintenance and in time in assembling of the conveyor, and the need for maintaining a substantial spare parts inventory is also reduced.
In one principal aspect of the present invention, a brake assembly comprises rotatable drive shaft means having a substantially cylindrical surface and torque tube means. The torque tube means also define a substantially cylindrical exterior surface and the drive shaft means extends axially into the torque tube means. The diameter of the cylindrical surface of the drive shaft means is slightly less than the internal diameter of the torque tube means such that the drive shaft means is capable of frictionally engaging the interior of the torque tube means to rotate the torque tube means when the drive shaft means is rotated, but is capable of slipping relative to the torque tube means when rotation of the torque tube means is restrained. Clamping surface means substantially surround at least a portion of the exterior surface of the torque tube means and the clamping surface means is movable relative to that exterior surface between a first position in which the clamping surface means is moved out of contact with the exterior of the torque tube means and the rotating drive shaft means rotates the torque tube means, and a second position in which the clamping surface means is moved into contact with the exterior of the torque tube means to restrain the torque tube means from rotating with the drive shaft means.
In another principal aspect of the present invention, the aforementioned torque tube means is formed of an organic polymer, preferably nylon, and the drive shaft is a hard metal, preferably steel.
In still another principal aspect of the present invention, at least one pulley is mounted on the exterior surface of the torque tube means and the pulley is axially movable on the torque tube means so as to frictionally engage the exterior surface of the torque tube means to rotate therewith when the torque tube means rotates. However, the pulley is rotationally slippable relative to the exterior surface of the torque tube means when the clamping surface means is moved to its second position.
In still another principal aspect of the present invention, the aforementioned brake assemblies are employed in combination with a plurality of live rotatable rollers for supporting and conveying an article along a plane and a plurality of endless resilient belts are looped about these rollers and the torque tube means to drive the rollers when the torque tube means is rotated by the drive shaft means.
In still another principal aspect of the present invention, trigger means are included in the last mentioned combination for sensing the presence of an article being conveyed by the rollers and control means are responsive to the trigger means to move the clamping surface means between its first and second positions, the trigger means, clamping surface means and torque tube means being constructed and arranged to operate the rollers in either a singulation mode or a slug mode.
These and other objects, features and advantages of the present invention will become apparent upon consideration of the detailed description of the invention to follow.